Their mum is here too. Will she show them how? This is all new to me and we really weren't expecting to ever have kittens. Our cat is from a rescue and was supposedly neutered, we found out this wasn't the case when we realised she was pregnant
Give the rescue a buzz and book Mum in for spaying as soon as they'll do it. Unfortunately, having young kittens won't stop another pregnancy if she gets out - and if she's a party girl, she'll get out somehow.
Oh - and Yes. She should teach them. (Although I'd be buying a stock of kitchen roll if you haven't already got some.)
I've just hand reared some kittens we found at about 3 weeks old, they started using the tray themselves at about 5-6 weeks, until then mum will help them wee and poo, and dispose of the evidence afterwards!!
<jealous of kittens- it's so sad that responsible cat owners never get the joy of kittens unless they are really lucky like the OP. Although I am probably supposed to say "oh how awful, how inefficient of the rescue place......." >
3 weeks is a little young but mum will show them when they're ready. I've got a litter of 6 week old kittens at the moment. My problem with litter training was that mum refuses to use a litter tray inside. Somehow though, they've picked it up pretty quickly. Still have the odd accident though